Intelligent serial battery charger and charging block

ABSTRACT

A serial battery charger including a number of serially connected battery charging sections in which the battery charging section is characterized by a first and second parallelly connected branches. The first branch includes terminals for connecting to the battery to be charged and a current blocking device and the second branch includes a by-passing switch which shunts across the terminals of the first branch when activated. The blocking device in the first branch prevents adverse reverse current flow from the battery to the charger when there is no power supply and also functions as a current block to prevent adverse flow of current from the battery into the shunting by-passing switch when the power supply to the charging section is in operation. This invention provides a simple solution to fulfil the conflicting requirements of an intelligent serial battery charger.

This application claims priority under 35 U.S.C. §§119 and/or 365 to01106195.9 filed in Hong Kong on Sep. 3, 2001; the entire content ofwhich is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to battery chargers for charging aplurality of rechargeable batteries connected in series. Moreparticularly, this invention relates to battery chargers having aplurality of serially connected battery charging sections. Morespecifically, although not solely limiting thereto, this inventionrelates to serial battery chargers in which a battery in any one of theserially connected charging sections can be removed or bypassed withoutmaterially affecting the charging conditions of the batteries remainingin other charging sections of the serial battery charger. Furthermore,this invention relates to serial battery chargers in which there isutilized a simple electronic element which provides a low-impedance tothe charging circuit during charging, a high-impedance to block reversecurrent flow from a battery when there is no power supply to thecharging section and a comparatively high-impedance when the chargingsection is shunted or by-passed.

BACKGROUND OF THE INVENTION

Re-chargeable batteries are widely used in a lot of portable or mobileelectrical and electronic devices or appliances such as, cellular orcordless telephones, remote repeaters, remote control units, remotesensors, portable lighting devices, portable radios, portable drills andmany other devices. Re-chargeable batteries are generally preferred overdisposable batteries nowadays because they are more environmentalfriendly and provide longer term cost savings. For remote applications,rechargeable batteries are probably the only practical choice.

Re-chargeable batteries require repeated charging in order to supplyelectrical power to the devices or appliances in which they areinstalled. Nowadays, portable devices usually require a plurality ofbatteries to operate and the batteries required are typically in therange of two to ten batteries. Hence, it is desirable that there can beprovided intelligent battery chargers which can charge a plurality ofre-chargeable batteries at the same time. There are two main types ofbattery chargers. The first type is the parallel charger in which allthe batteries are subject to the same charging voltage but are chargedwith different charging currents. The other type is the serial chargerin which the batteries being charged are connected in series and thesame charging current usually passes through all the serially connectedbatteries.

In applications in which batteries are alternatively charged anddischarged, a power supply of 3 to 12 volts is generally required whilethe voltage of each rechargeable battery is typically in the region of1-2 volts. In those applications, batteries are typically connected inseries for charging and discharging. For charging batteries for use insuch applications, a serial battery charger must be used.

Because of the wide-spread use of rechargeable batteries, there areincreasing demands for fast battery chargers which are capable of fullycharging an empty battery in about an hour (the “1C” chargers) so thatusers do not have to wait for too long before the batteries aresufficiently charged for use. For example, for a 1,600 mAH re-chargeablebattery, the 1C current rate is about 1.6A. In order to facilitate fastand efficient battery charging, battery chargers generally utilise highfrequency pulsed charging current having a relatively high current rate.When a battery is being charged, it will produce oxygen on the electrodeand the consumption of oxygen by the negative electrode will cause thebattery to heat up. In general, charging at the current rate of 1C ispreferred because this charging rate is regarded as striking a balancebetween reducing charging time and maintaining a healthy battery undercurrent battery technologies. Of course, with further advance in batterytechnologies, batteries may be charged at even higher current ratingswithout over-heating. If that happens, battery chargers supplying highercharging rating than 1C will be expected to become more popular. Ingeneral, fast battery chargers, especially those for charging smallvoltage re-chargeable batteries of about 1.5-2V, are preferablyconfigured so that the batteries are charged in series. This is becauseif the batteries are fast charged in parallel, a power supply having avery large current supply rating will be required and this may be verycostly.

On the other hand, a serial connection implies that the same currentmust flow through each serially connected charging section. This mayalso create great difficulty in a lot of circumstances. For example,when a battery is removed from the charger upon completion of chargingto avoid overheating or damaging or because it is already defective,charging will be disrupted until a replacement battery has been insertedinto the charger. Similar problems also arise if rechargeable batteriesof different capacities are charged together or good batteries are mixedwith bad ones. This is because when a battery of a smaller capacity hasbeen fully charged, there is a good chance that a battery of a largercapacity still requires charging. For simple serial chargers with nomonitoring and control circuits, the batteries will be continuouslycharged. As a result, overheating, battery damage or even explosion mayresult. On the other hand, for those more sophisticated serial batterychargers with charging conditions monitoring and charge controlcircuits, the battery charger may shut down once any one of thebatteries being charged is detected as being fully charged. This isobviously undesirable as the remaining batteries may still requirefurther charging. Furthermore, whenever batteries are inserted orremoved from a serial battery charger during the charging process, thewhole charging process will be interrupted. Hence, it is desirable ifthere can be provided intelligent serial battery chargers which allowserial charging of re-chargeable batteries in which the chargingcurrents supplied to the individual batteries in serial connection arelargely independent of that supplied to other batteries.

For many battery chargers, it is known that, when power supply to thebattery charger is turned off, there may be a reverse leakage currentwhich flows from the battery to the charger or the peripheral circuitry.Reverse leakage current among the serially connected batteries couldalso cause reverse charging of individual batteries by other batteriesthat are connected in the series charger. This is clearly undesirablewhich may cause draining of the full battery capacity and may evendamage the charger. Hence, it is desirable that each charging section ofa serial battery charger is provided with means to prevent undesirablereverse current leakage as well as a by-passing circuitry so that thecharging conditions of one individual charging section would not affectthe charging conditions of the other charging sections.

Many by-passing circuits, circuit arrangements or topologies have beenproposed to alleviate the adverse influence of the charging conditionsin a serial charging section to other charging sections. While serialchargers having arrangements to by-pass some or all of the chargingsections have been known, they are generally very complicated and do notsimultaneously include means or circuits to prevent reverse leakage ordischarge from the batteries.

To provide a serial battery charger which fulfils the above requirementsis a difficult task because several conflicting requirements need to bemet. Firstly, in order to prevent reverse current leakage or adversecurrent discharge from the battery, a blocking device which has a highreverse impedance must be inserted in series with the battery. Secondly,that serial block device must have a low impedance when there is aforward current which flows into the battery for battery charging. Onthe other hand, if the blocking device has a low forward impedance whenthe by-passing switch has been activated (which usually occurs whenthere is still power supply to the battery charging terminals), thatlow-impedance blocking device will compete with the by-passing switchfor the supplied current and, as a result, adverse charging current willkeep flowing into the batteries. In addition, that blocking device musthave a high impedance when the by-passing switch has been activated,otherwise, a large and un-desirable current will flow in a current loopwhich is formed by the battery, the blocking device and the by-passingswitch. Hence, it is highly desirable if a serial battery charger whichcan fulfil the above conflicting requirements can be provided. It willbe even more desirable if such improved battery chargers can be realisedusing simple circuit blocks and components so that high reliability aswell as low costs can be achieved.

OBJECT OF THE INVENTION

It is therefore an object of the present invention to obviate theproblems or shortcomings associated with existing or known serialbattery chargers. In particular, it is an object of the presentinvention to provide a circuit arrangement for an improved batterycharging section which can be used in serial chargers so that thecharging section can be shunted or by-passed when selected and, at thesame time, providing blocking means to prevent reverse current.

An important objective of the present invention is therefore to providean intelligent serial battery chargers in which the charging current orcharging conditions of one battery in the serial connection is largelyunaffected by the charging conditions of other batteries in the serialconnection.

An equally important object of the present invention is to provide aserial battery charger in which a battery can be removed from theserially connected battery at any time without disrupting the chargingof other batteries and, at the same time, adverse reverse current flowfrom a battery can be avoided.

As a minimum, it is an object of the present invention to provide thepublic with a choice of serial battery chargers which are provided meansto obviate undesirable battery discharge when the battery charger is notsupplying charging power and to provide useful battery by-pass whennecessary.

SUMMARY OF THE INVENTION

According to the present invention, there is provided an improvedserially connected battery charger which includes at least first andsecond parallelly connected branches, said first parallel branchincludes an electronically controllable by-passing switch and saidsecond parallel branch includes positive and negative terminals forreceiving respectfully the positive and negative terminals of a batteryand an one-way electronic device connected in series, said by-passingswitch has a very low impedance when turned-on and a very high impedancewhen turned-off, said one-way electronic device is characterised in thatit has a very low-impedance when current flows from said chargingsection into said battery terminals and it has a high-impedance whensaid by-passing switch is turned on.

According to another aspect of the present invention, there is provideda charging block for use in a serial battery charger including at leastfirst and second parallelly connected branches, said first parallelbranch includes an electronically controllable by-passing switch andsaid second parallel branch includes positive and negative terminals forreceiving respectfully the positive and negative terminals of a batteryand an one-way electronic device connected in series, said by-passingswitch has a very low impedance when turned-on and a very high impedancewhen turned-off, said one-way electronic device is characterised in thatit has a very low-impedance when current flows from said chargingsection into said battery terminals and a high-impedance when saidby-passing switch is turned on.

According to a third aspect of the present invention, there is provideda serial battery charger including a battery charging section whichincludes at least first and second parallely connected branches, whereinsaid first branch includes a diode serially connected with the terminalsfor connecting the battery to be charged and said second branch includesa MOSFET by-passing switch, said by-passing switch is connected acrosssaid first branch and provides low-impedance shunting when activated,said blocking diode has a low-impedance when current flows into saidbattery to be charged and has a high-impedance when there is no powersupply from said battery charger or when said by-passing switch isturned on.

According to a fourth aspect of the present invention, there is provideda battery charger including a plurality of battery charging sectionswhich are connected in series, wherein each said charging sectionincludes a first and a second parallelly connected branches, said firstparallel branch includes an electronically controllable by-passingswitch and said second parallel branch includes positive and negativeterminals for receiving respectfully the positive and negative terminalsof a battery and an one-way electronic device connected in series, saidby-passing switch has a very low impedance when turned-on and a veryhigh impedance when turned-off, said one-way electronic device ischaracterised in that it has a very low-impedance when current flowsfrom said charging section into said battery terminals and it has ahigh-impedance when said by-passing switch is turned on.

Preferably, the battery charger further including a micro-controller,the micro-controller monitors a set of parameters of the battery beingcharged and activates said by-passing switch by forming a low-impedanceshunting across said first parallel branch when some or all of saidmeasured battery parameters satisfies a set of pre-determinedconditions.

Preferably, the one-way electronic device is a diode.

Preferably, the by-passing switch is a field-effect-transistor (“FET”),including a MOSFET.

Preferably, the gate of said by-passing MOSFET is connected to amicrocontroller which controls the gate voltage of said MOSFET to turnon or turn off said MOSFET such that when said MOSFET is turned on, theimpedance across the drain-source terminals of said MOSFET is low,thereby activating the by-passing function, and, when said MOSFET isturned off, the impedance across the drain-source terminals is veryhigh, thereby de-activating the by-passing function.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be explained infurther detail by way of example and with reference to the accompanyingdrawings. In which:

FIG. 1 is a general block circuit diagram of the serial battery chargerof a preferred embodiment of the present invention.

FIG. 2 is a block diagram showing a specific example of the componentsused in each of the serial charging sections.

FIG. 3 is a general circuit diagram showing more connection particularsof the serial battery charging of FIGS. 1 and 2, and

FIG. 4 is a general circuit diagram showing more detailed hardwareconnection of a preferred embodiment of the present fast serial batterycharger.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is shown a block diagram showing a firstexample of a preferred embodiment of the present invention of anintelligent serial battery charger. The battery charger includes adirect current power source (100), a constant current source (200), amicro-controller unit (300) and plurality of battery charging sections(410, 420, 430 and 440) connected in series. The serially connectedbattery charging sections are connected to the positive and negativeterminals of the direct current power source (100) in order to obtain DCpower of the correct polarity.

Referring to FIG. 1, each of the charging sections (410, 420, 430 and440) includes an one-way electronic device which is connected in serieswith the positive and negative terminals of the battery in order tocontrol charging connecting to a battery. In order to provide acontrollable by-passing path which provides low impedance shuntingacross a charging section when necessary, for example, when the batteryin a particular charging section is fully charged, defective oroverheated, there is provided an electronic controllable switch (413) asshown in the Figure. The by-passing switch is connected in parallel withthe serial connection of the battery terminals and the one-wayelectronic device. The by-passing switch provides low impedance shuntingacross the terminals of the serial connection of the one-way electronicdevice and the battery terminals when activated. In the present specificembodiments, the by-passing switch is a three-terminal device in whichthe impedance across two of its terminals is controllable by a thirdterminal.

The one-way electronic device which is inserted in series with thebattery under charge should endeavour to fulfil the followingconflicting requirements. Firstly, it is preferred to have alow-impedance when the battery is being charged (that is, when forwardcurrent flows into the battery). Secondly, it is preferred to have ahigh-impedance when there is no power supply from the charger or, inother words, when the voltage at the battery terminals exceeds that ofthe charging terminals in order to prevent adverse discharge or reversecurrent flow from the battery, otherwise, the batteries will be drainedwhen there is no power supply from the direct current power source(100). Thirdly, the blocking device should have a very high impedancewhen the by-passing switch has been turned on because, otherwise, acurrent loop which is formed by the battery, the one-way device and theby-passing switch, may cause burning out of the circuit, since theby-passing switch should be of low-impedance in nature and the resultingcurrent in the current loop will be very large. In addition, theblocking device should have a considerably higher impedance than that ofthe activated by-passing switch (i.e. when it has been turned on) whenthe by-passing switch has been activated and when the voltage at thecharging terminals exceeds that of the battery, so that adverse currentwill not flow into the battery through the one-way electronic device.

In addition to merely providing a by-passing path, the combination ofthe electronically controllable by-passing switch together with theone-way electronic device allows high frequency and repeatedopen-circuit measurements across the battery terminals to be taken. Suchopen-circuit measurements are preferred in order to obtain sufficientbattery parameters to assess the charging conditions of a battery. Anexample of how the open-circuit electrical parameters of the batteriescan be taken will be explained below. For example, when themicro-controller (300) needs to read the open-circuit parameters of thebattery (422) which is being charged in the second serial charging block(420), it sends out electronic control signals through its I/O ports tothe control terminals of the three-terminal by-passing switches andturns on the by-passing switches 413, 433 and 443. As a result, theimpedance across the two other terminals of the by-passing switches 413,433 and 443 will be very low and the batteries 412, 432 and 442 will besubstantially by-passed because of the high impedance of the blockingdevice in this circumstances.

When the by-passing switches 413, 433 and 443 have been activated, ameasurement of the voltage taken across the positive terminal (A/D2 inFIG. 2) of the second battery (422) and the ground will give thecharacteristics of battery 422 only, since all the other batteries,namely, 412, 432 and 442, have been isolated from the measurementcircuitry because of the isolation by the blocking devices 411, 431 and441. It will be noted that, at this instant, the one-way electronicdevices 411, 431 and 441 will isolate the batteries 412, 432 and 442from the charging section and the open-circuit parameters of the battery422 can then be measured.

After measurements have been taken, the micro-controller again sends outanother control signal to the electronically controlled three-terminalswitches 413, 433 and 443 so that the impedance across the two otherterminals of the by-passing switches will again resume a high state tode-activate by-passing. As a result, current flows again through theone-way electronic device into the batteries being charged.

Alternatively, the second battery (422) can be measured by having thesecond by-passing switch (423) activated. At this instant, the secondbattery will be isolated and measurement can be taken across the batteryterminals directly. Of course, additional analogue-digital converterswill be needed to measure the potential difference across the twobattery terminals. To ensure accurate measurement of the open-circuitparameters, it is highly desirable that when the by-passing switches areclosed (activated), no current flows in or out of the batteries theassociated by-passing switches of which have been activated, otherwise,the open-circuit readings will not be accurate.

In order to prevent current from flowing out of the battery whenopen-circuit or close-circuit measurements are to be taken, the one-wayelectronic device should have a very high impedance which is sufficientto prevent current from flowing out of the battery in the reversedirection when by-passing is activated, even if the voltage at theterminals of the charging section before and after the activation of theby-passing switch is higher than that of the battery. Simultaneously, itis also preferred to prevent or minimise the current which may flow intothe battery terminals when the by-passing switch is turned on (or closedor activated, at which point the impedance across the two terminals ofthe by-passing switch is in the low state).

To prevent adverse flow of current from the power source into thebattery when the by-passing switch is closed, the impedance of theone-way electronic device (411, 421, 431, 441) when the by-passingswitch is closed should be significantly higher than that of theby-passing switch (413, 423, 433, 443). On the other hand, the one-wayelectronic device should have a very low-impedance where there iscurrent supply from the charger and when the by-passing switch is openedso that the charging current will entirely flow into the battery via theone-way electronic device for charging. To provide an electronicallycontrollable switch which has a high and a low-impedance state, a MOSFETis selected. In general, when a suitable gate voltage is applied to aMOSFET, the drain-source terminals of the MOSFET will become conductingwith low-impedance. On the other hand, if a different gate voltage isapplied, the drain-source terminals of the MOSFET will have a veryhigh-impedance and become non-conducting. A MOSFET switch is selected asa by-passing switch because it has a relatively high bandwidth so thatthe by-passing switch can be turned on and off many times within a shortperiod of time. Such repeated switching is required in order to take allthe necessary open circuit measurements and readings. The high bandwidthis also preferred in order to take responsive action once anyabnormality of a battery is observed and in order to minimise anynoticeable disruption to the other charging sections when a battery isremoved from the charger. Of course, other electronic devices exhibitingsimilar electronic characteristics may also be used as alternatives.

As regards the one-way electronic device, MOSFET also appeared to be asuitable candidate. In experiments to use a MOSFET as the one-waydevice, the micro-controller was programmed so that opposite effect gatevoltages are sent to the MOSFETs (one as one-way device and the other asby-passing switch). With such an arrangement, when one MOSFET is on, theother will be off and vice versa. Hence, when the one-way device isturned on, a low impedance path will be provided for the chargingcurrent. When the by-passing MOSFET is on, the one-way device will beoff, thereby forming a high impedance serial resistor isolating thebattery from the rest of the circuit.

Referring to FIG. 2, there is shown a preferred embodiment of thepresent invention in which a specific combination of an one-wayelectronic device and a by-passing switch are shown. In this embodiment,a MOSFET is used as a by-passing switch and a diode is used as anone-way electronic device. The diode is connected in series with thebattery terminals in the manner as shown in FIG. 2 so that chargingcurrent can flow into the battery through a low-impedance path whilereverse current flow is blocked. When the MOSFET by-passing switch (413,etc.) is turned on, the drain-source impedance becomes very low and thedrain-source voltage is therefore also very low which is typically inthe region of 0.2 volt. Since such a low voltage across the drain andsource terminals is far from the turn-on voltage of the diode which istypically in the region of 0.6 volt, the diode becomes a high-impedanceblocking device which prevents current from flowing into the battery. Bythe synergetic utilization of the combined characteristics of the twodevices, namely, the low drain-source voltage of about 0.2 volt when aMOSFET is turned on and the high turn-on voltage of about 0.6 volt for adiode, a battery charger or battery charging section satisfying theafore-said conflicting requirements can be provided. As shown in theFigures, a plurality of charging sections can be connected in series inorder to provide a preferred serial charger.

Referring to FIG. 3, there is shown a schematic diagram showing moredetailed connection between the power source (100), current source(200), CPU (300) and the serially connected charging sections (410, 420,430, 440). Each of the charging section includes a blocking diode (411,etc.) which prevents reverse flow of current out of the battery as wellas providing a high-impedance isolation of the battery terminals whenthe low-impedance switch (413, etc.) is turned on, even though at thatinstant, the diode is under a small forward bias. In this specificembodiment and as shown in FIG. 3, each charging section is providedwith receptacles for alternatively charging a AAA or a AA battery.

Referring to FIG. 4, there is shown a more detailed circuit arrangementsof the charging sections of FIG. 3. In this specific embodiment, theby-passing MOSFETs, the blocking diodes as well as the MOSFET gatecontrolling circuitry which is connected between the by-passing MOSFETsand the CPU is described in more detail. This gate control circuitry isintended to provide only a working example of the control of theby-passing switch, many other circuit variations are of course possibleto achieve substantially same or similar effects.

While the present invention has been explained by reference to thevarious specific examples described above, it should be appreciated thatthose examples are merely provided to assist understanding only andshould not in any way be used to limit or restrict the scope of thepresent invention. In addition, it should be appreciated that the scopeof the present invention shall be interpreted according to the spirit ofthe invention as described in the above description and should thereforecover modifications or variations which are obvious or trivial topersons skilled in the art. In particular, the present invention hasdisclosed a synergetic utilization of a combination of rather simplecomponents to proffer a circuitry or circuit arrangements in which thevarious conflicting requirements for battery charging sections areaccommodated and provided in a very simple way and by using relativesimple components and in a simple arrangement.

1. A serial battery charger including a charging section which includesat least first and second parallelly connected branches, said firstparallel branch includes an electronically controllable by-passingswitch and said second parallel branch includes positive and negativeterminals for receiving respectfully the positive and negative terminalsof a battery and an one-way electronic device connected in series, saidby-passing switch has a very low impedance when turned-on and a veryhigh impedance when turned-off, said one-way electronic device ischaracterised in that it has a very low-impedance when current flowsfrom said charging section into said battery terminals and it has ahigh-impedance when said by-passing switch is turned on.
 2. A batterycharger according to claim 1, further including a micro-controller tomonitor at least one parameter of the battery being charged and activatesaid by-passing switch by forming a low-impedance shunting across saidfirst parallel branch when one or more of said measured batteryparameters satisfies a pre-determined condition.
 3. A battery chargeraccording to claim 2, wherein said battery parameter include any one ormore of the following parameters: -open-circuit voltage, close-circuitvoltage and the temperature of said battery.
 4. A battery chargeraccording to claim 3 15, wherein said battery parameters further includethe detection of the type and presence of a battery.
 5. A batterycharger according to claim 1 15, wherein said one-way electronic deviceis a diode.
 6. A battery charger according to claim 1 15, wherein saidby-passing switch is a field-effect-transistor (“FET”), including aMOSFET.
 7. A battery charger according to claim 6, wherein said gateterminal of said FET is connected to said micro-controller foractivating and de-activating said by-passing switch.
 8. A charging blockfor use in a serial battery charger including at least first and secondparallelly connected branches, said first parallel branch includes anelectronically controllable by-passing switch and said second parallelbranch includes positive and negative terminals for receivingrespectfully the positive and negative terminals of a battery and anone-way electronic device connected in series, said by-passing switchhas a very low impedance when turned-on and a very high impedance whenturned-off, said one-way electronic device is characterised in that ithas a very low-impedance when current flows from said charging sectioninto said battery terminals and a high-impedance when said by-passingswitch is turned on.
 9. A charging block according to claim 8, furtherincluding a micro-controller to monitor at least one parameter of thebattery being charged and activate said by-passing switch by forming alow-impedance shunting across said first parallel branch when one ormore said measured battery parameters satisfies a pre-determinedcondition.
 10. A serial battery charger including a battery chargingsection which includes at least first and second parallely connectedbranches, wherein said first branch includes a diode serially connectedwith the terminals for connecting the battery to be charged and saidsecond branch includes a MOSFET by-passing switch, said by-passingswitch is connected across said first branch and provides low-impedanceshunting when activated, said blocking diode has a low-impedance whencurrent flows into said battery to be charged and has a high-impedancewhen there is no power supply from said battery charger or when saidby-passing switch is turned on.
 11. A battery charger according theclaim 10, wherein the gate of said by-passing MOSFET is connected to amicro-controller which controls the gate voltage of said MOSFET to turnon or turn off said MOSFET such that when said MOSFET is turned on, theimpedance across the drain-source terminals of said MOSFET is low,thereby activating the by-passing function, and, when said MOSFET isturned off, the impedance across the drain-source terminals is veryhigh, thereby de-activating the by-passing function.
 12. A batterycharger including a plurality of battery charging sections which areconnected in series, wherein each said charging section includes atleast first and second parallelly connected branches, said firstparallel branch includes an electronically controllable by-passingswitch and said second parallel branch includes positive and negativeterminals for receiving respectfully the positive and negative terminalsof a battery and an one-way electronic device connected in series, saidby-passing switch has a very low impedance when turned-on and a veryhigh impedance when turned-off, said one-way electronic device ischaracterised in that it has a very low-impedance when current flowsfrom said charging section into said battery terminals and it has ahigh-impedance when said by-passing switch is turned on.
 13. A batterycharger according to claim 12, further including a micro-controller tomonitor at least one parameter of the battery being charged and activatesaid by-passing switch by forming a low-impedance shunting across saidfirst parallel branch when one or more of said measured batteryparameters satisfies a pre-determined condition.
 14. A battery chargeraccording to claim 12, wherein said one-way electronic device is adiode.
 15. A serial battery charger for charging a plurality of discretebatteries, the battery charger comprising: a charging current source, aplurality of battery charging sections connected in series for charginga corresponding plurality of discrete batteries, and a micro-controller;wherein each one of said battery charging sections comprises first andsecond branches which are connected in parallel, said first parallelbranch including an electronically controllable bypassing switch, andsaid second parallel branch comprising a positive terminal and anegative terminal for receiving respectively the positive and negativeterminals of a battery and a one-way electronic device connected inseries; wherein each said bypassing switch has a very low impedance whenturned-on and a very high impedance when turned-off, wherein each saidone-way electronic device has a very low impedance to a battery chargingcurrent which flows from said current source into the positive batteryterminal, and said one-way electronic device has a very high impedancewhen said bypassing switch is turned on, and wherein saidmicro-controller is configured so that the bypassing switch of a batterycharging section is activated to form a low-impedance shunt across thatbattery charging section upon physical removal of a battery from thatbattery charging section to permit charging of other batteries in otherbattery charging sections of said battery charger to continue.
 16. Aserial battery charger according to claim 15, wherein the bypassingswitches of said plurality of charging sections are repeatedly activatedduring a battery charging process for assessing charging parameters of abattery.
 17. A serial battery charger according to claim 16, whereinsaid bypassing switches are repeatedly activated by saidmicro-controller at a high frequency.
 18. A serial battery chargeraccording to claim 16, wherein said micro-controller and said bypassingswitches of said plurality of battery charging sections are adapted sothat said bypassing switches are repeatedly and individually actuatableduring battery charging to enable the charging conditions of batteriesconnected to said plurality of battery charging sections to be assessed.19. A serial battery charger according to claim 15, wherein saidmicro-controller and said bypassing switches of said plurality ofbattery charging sections are configured so that said bypassing switchesare repeatedly actuated during battery charging, to assess chargingconditions of batteries connected to said plurality of battery chargingsections.
 20. A serial battery charger according to claim 19, whereinsaid bypassing switches of said plurality of battery charging sectionsare selectively actuatable during a battery charging process, forindividually monitoring the charging conditions of batteries connectedto said plurality of battery charging sections.
 21. A serial batterycharger according to claim 19, wherein said micro-controller and saidbypassing switches are adapted so that the bypassing switch of a batterycharging section is activated when one parameter of a battery connectedto said battery charging section satisfies a pre-determined condition.22. A serial battery charger according to claim 19, wherein, uponactuation of a bypassing switch of a selected battery charging section,said one-way electronic device of said selected battery charging sectionbecomes current blocking, whereby a battery connected to said selectedbattery charging section is effectively isolated from both said firstand second parallel branches.
 23. A serial battery charger according toclaim 19, wherein said micro-controller and said bypassing switches areadapted so that, when a battery is removed from a battery chargingsection, or when the terminal voltage of a battery is to be measured,the bypassing switch of said battery charging section is actuated.
 24. Aserial battery charger according to claim 19, wherein the bypassingswitch of a selected battery charging section is actuated upon detectionof a battery terminal voltage exceeding the supply voltage of saidselected battery charging section.
 25. A serial battery chargeraccording to claim 19, wherein said one-way electronic device isdisposed against discharge of a battery through said second parallelbranch.
 26. A battery charger according to claim 15, wherein the currentrating of said charging current source is at a rate of 1C or above, andwherein said micro-controller and said bypassing switches of saidplurality of charging sections are arranged for high-frequency switchingand are selectively activatable.
 27. A battery charger according toclaim 26, wherein said bypassing switch, comprises a MOSFET, and saidone-way electronic device comprises a blocking diode, said blockingdiode having a low-impedance when current flows into the battery beingcharged and a high-impedance when there is no power supply from saidbattery charger.
 28. A battery charger according to claim 15, whereinsaid bypassing switches of said plurality of battery charging sectionsare individually activatable and deactivatable, and wherein a batteryconnected to a battery charging section with the bypassing switchactivated is effectively isolated from the circuitry of said chargingsection.
 29. A battery charger according to claim 28, wherein saidone-way electronic device is a blocking diode and said bypassingswitching is controlled by said micro-controller.
 30. A battery chargeraccording to claim 28, further comprising voltage measuring means,wherein said micro-controller, said voltage measuring means, saidone-way electronic devices and said bypassing switches are adapted forhigh-frequency and repeated voltage measurements of batteries connectedto said battery charging sections.
 31. A battery charger according toclaim 30, wherein the voltage of a battery connected to a selectedbattery charging section is measured upon isolation of said battery fromsaid selected battery charging section by activation of the bypassingswitch of said selected battery charging section.
 32. A serial batterycharger according to claim 16, wherein said charging current source isadapted for charging batteries at a charging current rate of 1C andabove, said bypassing switches are individually controllable by saidmicro-controller, and said bypassing switches are adapted forhigh-frequency switching so that the charging conditions of a batterycan be monitored during the entire battery charging process.
 33. Abattery charger according to claim 15, wherein said micro-controller isalso configured for monitoring at least one parameter of a battery beingcharged in a battery charging section and for activating the bypassingswitch of a battery charging section by forming a low-impedance shuntingacross the first parallel branch of that battery charging section whenone of said parameters of the battery connected to that battery chargingsection satisfies a pre-determined condition, said battery parametersincluding open-circuit voltage, close-circuit voltage and thetemperature of said battery.
 34. A battery charger according to claim15, wherein each charging section is for charging an AA or an AAAbattery.
 35. A battery charger according to claim 15, wherein saidbypassing switch is activated to form a low-impedance shunt across oneof the battery charging sections upon detection of overheating of abattery from that battery charging section of the battery charger sothat charging of batteries in other battery charging sections of saidbattery charger continues.
 36. A battery charger according to claim 15,wherein said bypassing switch activated to form a low-impedance shuntacross one of the battery charging sections upon detection of adefective battery in that battery charging section of the batterycharger so that charging of batteries in other battery charging sectionsof said battery charger continues.
 37. A battery charger according toclaim 15, wherein said bypassing switch is activated to form alow-impedance shunt across one of the battery charging sections upondetection of a fully charged battery in that battery charging section ofthe battery charger so that charging of batteries in other batterycharging sections of said battery charger continues.
 38. A batterycharger according to claim 15, wherein said bypassing switch isrepeatedly activated to form a low-impedance shunt across one of thebattery charging sections for battery voltage measurements during abattery charging process.
 39. A battery charger according to claim 15,wherein said battery charger comprises a constant current source.
 40. Abattery charger according to claim 15, wherein said micro-controller isfurther configured so that the bypassing switch of a battery chargingsection is activated to form a low-impedance shunt across that batterycharging section when a defective or an overheated battery is present inthat battery charging section to permit charging of other batteries inother battery charging sections of said battery charger to continue. 41.A battery charger according to claim 15, wherein said micro-controlleris further configured so that the bypassing switch of a battery batterycharging section is operated to permit charging of said battery whensaid battery is inserted into that battery charging section.